This application concerns production of ethanol and, more particularly, to conversion of biomass for producing ethanol. The invention is particularly applicable to conversion of wood and agricultural wastes to produce ethanol. However, it will be appreciated that certain aspects of the invention have broader applications.
The Scholler, Madison and Bergius acid hydrolysis processes for the manufacture of ethanol from abundant wood waste have been proposed and/or practiced in the past. However, all are considered uneconomical due mainly to either being highly capital intensive with associated high operating costs, or to the low yields obtained. Recent technology, such as the enzymatic Gulf process and the Stake technology, show substantial improvement in yield, but yet remain capital intensive.
Citrus residue (peel, pulp and seed), another abundant biomass source, is presently processed, in a marginally profitable operation, to produce animal feed and citrus molasses. This operation is necessitated to alleviate a serious disposal problem. In the State of Florida alone, over one million tons of dried citrus pulp and pellets are produced annually which is equivalent to the processing of nearly eight million tons of citrus residue. Additional large tonnages are processed in California, Arizona and Texas.
The citrus peel, including pulp, rag and seed, is presently shredded, and treated with an alkaline slurry or powder, such as lime, intimately contacted in a special mixer, and is then pressed to release a "press liquor," thereby reducing the water content of the peel. This in turn reduces the heat load on the dryers which subsequently produce the dried animal feed. The pressed liquor is evaporated to produce a citrus molasses which is either blended with the peel in the drying operation, or is sold separately for production of other byproducts. Citrus culls are disposed of in a similar manner.
In the present state of the art, the small amount of citrus molasses produced in the above-noted operations is used as feedstock to produce ethanol. None is presently produced from wet peel.
Wood and agricultural wastes, such as citrus peel, are in abundance and, therefore, appear to be the best and cheapest feedstocks for ethanol production, providing that an economical process for obtaining a high yield can be found. Cheaper ethanol can then replace the lead phased out of the gasoline pool as the octane booster. Citrus peel can replace citrus molasses as a feedstock for manufacture of beverage or anhydrous ethanol, and provide a substantially higher yield, on a per ton of peel basis.